Electron microscope and electron microscopy method

ABSTRACT

An electron microscope for observing a magnetization state of a specimen with high resolution and an electron microscopic method. The electron microscope comprises an electron beam irradiating device including a scanning coil 3 and an objective lens 4 to irradiate an electron beam 2 emitted from an electron source 1 on a desired part of a specimen 51, and a circularly polarized light detector including a quarter wave plate 8, a polarizer 9 and a photodetector 11 to detect circularly polarized light generated from the electron beam irradiated part of the specimen 51. Since the intensity of the circularly polarized light generated from the specimen irradiated with the electron beam depends on the direction of magnetization in the electron beam irradiated part and the detecting direction, the distribution of magnetization can be measured by observing a scanning image in the form of a luminance signal indicative of the intensity of the circularly polarized light while scanning the electron beam irradiated part on the surface of the specimen.

TECHNICAL FIELD

The present invention relates to electron microscopes and electronmicroscopic methods and more particularly, to an electron microscope andan electron microscopic method which are suitable for observing amagnetization state of a magnetic specimen of desired thickness withhigh resolution.

BACKGROUND ART

As techniques of observing a magnetization state of a magnetic specimenby means of an electron microscope, a method for detection of Lorentzdeflection of an electron beam transmitting through the specimen(Lorentz electron microscope) or a method for detection of spinpolarization of secondary electrons (spin polarization SEM) has beenused. Of them, the Lorentz electron microscope is described in, forexample, Surface Science, Vol. 13, pp. 525-532 (1992) and the spinpolarization SEM is also described in Surface Science, Vol. 13, pp.512-527 (1992).

DISCLOSURE OF INVENTION

Of the above prior arts, the Lorentz electron microscope faces atechnical problem that before observation of the specimen, the specimenmust be formed in advance into a film thin enough for an electron beamto transmit therethrough. Lorentz deflection of reflection electrons andsecondary electrons can be detected (the magnetization state can beobserved) without forming the specimen into a thin film but in thatcase, the change of detection signal due to Lorentz deflection becomesslight, raising a technical problem that full play cannot be given tohigh spatial resolution inherently owned by the electron microscope.

On the other hand, the aforementioned spin polarization SEM can affordto observe the magnetization state with high resolution without formingthe specimen into a thin film but there needs special electron opticalsystem and detector for detection of spin polarization of secondaryelectrons, raising a technical problem that the apparatus is inevitablycomplicated and increased in scale. In addition, the signal is sensitiveto the surface condition of the specimen, also raising a technicalproblem that the function of applying the surface cleaning process tothe specimen and a vacuum evacuation unit of high performance formaintaining the cleaned surface condition during observation are needed.

The present invention is made to solve the above-described problems andit is an object of the present invention to provide an electronmicroscope which can perform high-resolution observation of amagnetization state of a specimen without applying the complicatedprocess of thin film forming and surface cleaning to the specimen andwhich can be simplified in equipment construction.

To accomplish the above object, in the present invention, in place ofthe electron detecting method of prior art, circularly polarized light,that is, light (an electromagnetic wave) having a polarization planewhich rotates about an axis in the propagating direction, generated froman electron beam irradiated part of a specimen, especially, a magneticspecimen is detected. More specifically, an electron microscopecomprises means for holding a specimen, means for irradiating anelectron beam on the specimen (usually including an electron source andan electron optical system), and means for detecting an electromagneticwave of circular polarization (so-called circularly polarized light)generated especially from an electron beam irradiated part of thespecimen. Preferably, the circularly polarized light detecting means isprovided between the specimen holding means (for example, a specimenholder) and the electron optical system of the electron beam irradiatingmeans. Preferably, a power supply for applying a voltage between thespecimen (or specimen holding means) and the electron optical system isprovided.

In order to increase the generation efficiency of the circularlypolarized light, energy of the irradiating electron beam is made to below, preferably, 100 eV or less. Accordingly, in addition to thefunction of irradiating an electron beam on a desired part of a specimenas in the ordinary electron microscope, the present invention has thefunction of decelerating the electron beam to the aforementioned energyrange immediately before the electron beam reaches the specimen and thefunction of detecting, in a specified direction, circularly polarizedlight generated from the electron beam irradiated part. Detection of thecircularly polarized light is carried out by a combination of, forexample, a quarter wave plate, a polarizer and a light intensitydetector.

When the electron beam is irradiated on a solid specimen, electrons inthe solid specimen are excited either to move to a higher energy levelor to be emitted from the solid specimen. When electrons moved to thehigher energy level in the solid specimen return to the original orlower energy level (perform transition), energy corresponding to adifference between these energy levels is emitted (so-called energyrelaxation process). As a mode of the energy emission, there is, forexample, emission of an electromagnetic wave from the solid specimen.The above phenomenon is utilized to make available a known X-raymicroanalyzer for measuring characteristic X-rays of a solid specimenwhich represent electromagnetic waves generated under the electron beamirradiation on the solid specimen and a known cathode ray luminescencemethod (cathode luminescence: CL method) for measuring luminescencegenerated when excited electrons are captured by a localized level inthe solid specimen (recombination). In these techniques, an equipmentfor spectroscopic analysis (energy analysis) of electromagnetic wavesgenerated from the specimen is used.

Incidentally, under the irradiation of the electron beam on the magneticspecimen, some of electrons in the magnetic specimen are excited to avalence electron state at an energy level which is several eV higherthan the Fermi level and they have such a nature that when being againreturned to the ground state, they emit circularly polarized light inthe direction of magnetization (magnetic circular dichroism; MCD). Thepresent invention applies this nature to high resolution observation ofa magnetization state of the specimen and features measurement of acircular polarization (circularly polarized light) of electromagneticwaves generated from the specimen.

Some of electrons in the magnetic specimen irradiated with the electronbeam are excited to an energy level other than the valence electronstate (for example, excited to plasmon) and the individual modes ofexcitation are liable to occur depending on the energy of the irradiatedelectron beam (for example, a voltage for accelerating the electron beamfrom the electron source toward the specimen). Accordingly, by loweringthe energy of the irradiating electron beam to, preferably, 100 eV orless as described previously to suppress excitation of higher energythan valence electron excitation (excitation to other states than thevalence electron state) including the plasmon excitation, circularlypolarized light due to MCD can be generated highly efficiently from theelectron beam irradiated part.

The circularly polarized light generated by such a mechanism as above isa light ray of several eV in terms of photon energy, that is, in therange of from infrared to ultraviolet. Accordingly, its intensity can bedetected easily by first changing the circularly polarized light tolinearly polarized light by means of the quarter wave plate and thenguiding the linearly polarized light to a photodiode or photomultipliertube through a polarizer. With the quarter wave plate and polarizerprovided in the optical system for detecting the circularly polarizedlight, linearly polarized light in light rays which act as backgroundnoise on the magnetization state measurement of the specimen can bechanged, by means of the quarter wave plate, to circularly polarizedlight and can be shielded (prevented from coming into the detector) bythe polarizer.

The intensity of the thus obtained circularly polarized light (namely, alight ray having magnetization state information of the specimen) ismaximized when the direction of magnetization in the electron beamirradiated part coincides with the detecting direction and is decreasedas the direction of magnetization deviates from the detecting direction.Accordingly, by observing a scanning image in the form of a luminancesignal indicative of the circularly polarized light intensity whilescanning the electron beam irradiated part on the surface of thespecimen, a state of distribution of magnetization can be known.

Needless to say, the specimen is not required to be formed into a thinfilm for the purpose of detection of the circularly polarized light.Further, since the emission of the circularly polarized light is notaffected by details of the surface condition, the highly graded surfacecleaning process is not needed. In addition, the aforementionedsimplified optical system suffices for detection of the circularlypolarized light and hence, the apparatus will not be increased in scaleand remarkably complicated by the incorporation of the optical system.As a result, the electron optical system for irradiating the electronbeam on the specimen can be of the construction optimized forrealization of high resolution.

As described above, according to the present invention, high-resolutionobservation of the magnetization state can be ensured with thesimplified equipment construction without applying to the specimen anyspecial process for observation. And besides, the number of units to beadded for the observation to the electron microscope is small andtherefore, compatibility with the other observing function which isexpected from the ordinary electron microscope is facilitated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining a first embodiment of the presentinvention.

FIG. 2 is a diagram for explaining a second embodiment of the presentinvention.

FIG. 3 is a diagram for explaining application examples of the first orsecond embodiment.

FIG. 4 is a diagram for explaining an application example of the firstor second embodiment of the present invention.

FIG. 5 is a diagram for explaining a third embodiment of the presentinvention.

FIG. 6 is a diagram for explaining application examples of the thirdembodiment of the present invention.

FIG. 7 is a diagram for explaining a fourth embodiment of the presentinvention.

FIG. 8 is a diagram for explaining application examples of the fourthembodiment.

FIG. 9 is a diagram for explaining a fifth embodiment of the presentinvention.

FIG. 10 is a diagram for explaining a sixth embodiment of the presentinvention.

FIG. 11 is a diagram for explaining an application example of the sixthembodiment of the present invention.

FIG. 12 is a diagram for explaining a seventh embodiment of the presentinvention.

FIG. 13 is a diagram for explaining an eighth embodiment of the presentinvention.

FIG. 14 is a diagram for explaining flow of the processing in the eighthembodiment of the present invention.

FIG. 15 is a diagram for explaining a ninth embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described hereinafter in greater detail byreferring to embodiments shown in the drawings. It is to be noted thatidentical reference numerals in FIGS. 1 to 15 denote identical orsimilar components.

FIG. 1 is a diagram showing the construction of an essential part of afirst embodiment of the present invention. In the figure, an electronbeam 2 emitted from an electron source 1 and accelerated to 20 keV byelectron lenses 22 and 23 is directed to a specimen 51 held on aspecimen holder 5 through an electron optical system including ascanning coil 3 and an objective lens 4 which are illustrated insimplified form in the figure. The specimen 51 is held on the specimenholder 5 in either placing or holding manner. The electron source 1 isapplied with a high voltage of -20 keV relative to the succeedingelectron lens 23 at earth potential by means of power supplies 24 and25. Accelerating energy of the electron beam 2 is determined by apotential difference between electron source 1 and electron lens 23which is set by these power supplies 24 and 25, and a value other than20 keV (for example, a desired value lying between 1 and 50 keV) canalso be used. The electron beam 2 is decelerated immediately beforereaching the specimen holder 5 by means of a unit 21 for applyingpotential between the objective lens 4 (earth potential) and thespecimen holder 5 and is irradiated, at energy which is set to a desiredlevel of 200 eV or less, on the specimen 51 placed on the specimenholder 5. In this manner, even when the energy of the electron beam 2incident upon the specimen 51 on the specimen holder 5 is low, theelectron beam 2 emitted from the electron source 1 is once acceleratedto higher energy than the incident energy so as to be passed through theelectron optical system and is then decelerated to a desired energylevel immediately before the incidence upon the specimen 51. This is awell-known technique for performing high-resolution observation byfocusing the electron beam 2 to a thin beam.

Light emitted from a part of specimen 51 upon which the electron beam 2is incident is collected by a condenser lens 6 and then passedsequentially through an interference filter 7, a quarter wave plate 8and a polarizer 9 before reaching a photodetector 11 via a focusing lens10. In the present embodiment, an avalanche diode is used as thephotodetector 11 but another photodetector such as a photomultipliertube or a CCD may be used. Further, in the present embodiment, aninterference filter 7 having bandwidth of 50 nm is ordinarily used byclosing the appropriate one in accordance with a wavelength of light tobe detected. But, depending on the allowable range of wavelength of thelight to be detected, an interference filter of anther bandwidth may beused or sometimes, wavelength selection is unneeded and no interferencefilter is used.

When strict wavelength selection is necessary, a spectrometer 12carrying a prism and a diffraction grating is utilized in place of theinterference filter 7 as shown in a second embodiment of the presentinvention illustrated in FIG. 2. In this case, a condenser lens 6, aquarter wave plate 8, a polarizer 9, a focusing lens 10, thespectrometer 12 and a photodetector 11 are arranged in this order toconstitute a circularly polarized light detecting system. By using thespectrometer 12 in the circularly polarized light detecting system, anadvantage that the exchange of interference filter 7 to conform with awavelength of light is not necessary can be attained. Incidentally, whenthe spectrometer 12 is used to constitute the circularly polarized lightdetecting system, a resulting system is more increased in occupationvolume than the circularly polarized light detecting system using theinterference filter 7. Then, if this matters, the light from thefocusing lens 10 will once be guided to an optical fiber 13 so as to betransmitted to the spectrometer 12 installed at a location free fromspatial restriction as in the case of the present embodiment shown inFIG. 2.

The provision of a wavelength selecting means such as interferencefilter 7 and spectrometer 12 in a light detecting means for detection oflight from the specimen 51 is effective for suppressing noise indetection of circularly polarized light of a desired (measuring object)especially when the light generated from the specimen 51 contains lightrays of various wavelengths. When the circularly polarized light has awavelength equal or nearly equal to that of the other light (so-callednoise), the two light rays can be separated from each other by means ofthe quarter wave plate 8 and polarizer 9. But, when circularly polarizedlight of the measuring object and light of a wavelength different fromthat of the circularly polarized light are emitted from the specimen 51,the light of different wavelength cannot be separated from thecircularly polarized light of measuring object by means of the quarterwave plate 8 and polarizer 9 regardless of the light of differentwavelength being of a linear polarization or a circular polarization.This is because the function of converting a linear polarization into acircular polarization or vice versa depends on a wavelength passingthrough the wave plate.

Next, measurement examples by the first embodiment of the presentinvention shown in FIG. 1 or the second embodiment of the presentinvention shown in FIG. 2 will be depicted in FIG. 3. FIG. 3 graphicallyillustrates results of measurement of dependency of the signal intensityupon the wavelength of circularly polarized light when a cobalt (0001)thin film epitaxially grown on a gold substrate is used as specimen 51and energy of the electron beam 2 incident on the specimen 51 is 5 eVand 150 eV. It should be noted that the signal intensity in FIG. 3 isnormalized by current of the electron beam 2 incident on the specimen 51and luminescent efficiency at individual wavelengths. As is clear fromFIG. 3, the dependency of the signal intensity upon the wavelengthdiffers with different incident energy levels of the electron beam 2 andthe average signal intensity for an incident energy level of 150 eV ofthe electron beam 2 is only a fraction of that for 5 eV. This is becauseas the incident energy of the electron beam 2 increases, excitation tohigher energy than valence electron excitation, such as plasmonexcitation, becomes active and the efficiency of generation ofcircularly polarized light due to MCD is decreased. Accordingly, it hasbeen proven that the incident energy of the electron beam 2 is 100 eV orless and more preferably, 10 eV or less.

Next, results of observation of scanning images performed using a cobalt(0001) thin film epitaxially grown on a gold substrate as the specimen51, as in the case of FIG. 3, in accordance with the first embodiment ofthe present invention shown in FIG. 1 and the second embodiment of thepresent invention shown in FIG. 2 are diagrammatically shown in FIG. 4.Incident energy of the electron beam 2 is set to 10 ev. Contrast ofimages in FIG. 4 represents the normalized intensity of circularlypolarized light at individual locations, that is, the component ofmagnetic moment in the observation direction, demonstrating thatdistribution of magnetization states of the specimen 51 is captured asimages.

Next, a third embodiment of the present invention will be described withreference to FIG. 5. In FIG. 5, a magnetic field applying unit 14 forpermitting application of a controlled external magnetic field to thespecimen 51 is added to the construction of the first embodiment of thepresent invention described with reference to FIG. 1. With thisconstruction, a response of the magnetization state to the externalmagnetic field can be measured at individual parts of the specimen 51.FIG. 6 shows results of measurement at two points on the specimen 51(shown as points A and B in FIG. 6) carried out using, as the specimen51, a polycrystal cobalt thin film grown on a chromium underlayerthrough spattering process. As is clear from measurement examples ofFIG. 6, a local magnetization curve can be obtained at a desiredlocation on the specimen 51 according to the third embodiment of thepresent invention shown in FIG. 5.

Next, a fourth embodiment of the present invention will be describedwith reference to FIG. 7. In FIG. 7, a temperature controlling unit 15capable of setting the specimen 51 at a predetermined temperature isadded to the construction of the first embodiment of the presentinvention described with reference to FIG. 1. With this construction,dependency of the magnetization state upon temperatures can be measuredat individual parts of the specimen 51. FIG. 8 shows results ofmeasurement at two points on the specimen 51 (shown as points A and B inFIG. 8) carried out using, as the specimen 51, a polycrystal cobalt thinfilm grown on a chromium underlayer through spattering process as in thecase of FIG. 6. As is clear from the measurement examples of FIG. 8,temperature characteristics of the magnetization state including Curietemperature at desired locations on the specimen 51 can be obtainedaccording to the embodiment of the present invention shown in FIG. 7.

Next, a fifth embodiment of the present invention will be described withreference to FIG. 9. In FIG. 9, a specimen scanning unit 16 comprised ofa piezo-actuator is added to the construction of the first embodiment ofthe present invention described with reference to FIG. 1. This ensuresthat a scanning image in the form of a luminance signal indicative of asignal from the photodetector 11 can be obtained by not only a method ofscan-moving the electron beam 2 on the surface of specimen holder 5 bymeans of the scanning coil 3 but also a method of scan-moving thespecimen holder 5 in relation to the electron beam 2. In the fifthembodiment of the present invention shown in FIG. 9, a point at whichcircularly polarized light is generated can always be immobile byscanning the specimen holder 5 without performing scanning of theelectron beam 2, thereby attaining an advantage that the detectionaccuracy of the intensity of circularly polarized light can be improved.In the case of scanning (movement) of the specimen holder 5, theluminance signal is fetched in correspondence to, preferably, insynchronism with the scanning of the specimen holder 5. This resemblesthe fetching of the luminance signal carried out in correspondence tothe scanning of the electron beam 2 when the electron beam 2 is scanned.

To obtain the magnetization state distribution in the form of images,still another method (circularly polarized light imaging method) canalso be considered in which the electron beam 2 is irradiated on thewhole observation area of the specimen 51 while not being focused andthe optical system for detection of circularly polarized light is usedas an imaging system to image the intensity of circularly polarizedlight at individual parts of an image. Substitution of an imaging typedevice such as for example a CCD (charge coupled device) for thephotodetector 11 suffices for this purpose and besides, the electronoptical system can be more simplified than that of the embodiments ofthe present invention which have been set forth so far or can bedispensed with thoroughly. But the resolution of images obtained throughthis circularly polarized light imaging method is prescribed by thewavelength of detected light and therefore, resolution comparable tothat obtained through the method of obtaining images by focusing theelectron beam cannot be accomplished. Accordingly, it is desirable thatthe circularly polarized light imaging method be used only whenobservation of the magnetization state distribution is desired to becarried out in a simple way by using an apparatus of compactconstruction.

Next, a sixth embodiment of the present invention will be described withreference to FIG. 10. In FIG. 10, to the construction of the firstembodiment of the present invention described with reference to FIG. 1,another circularly polarized light detecting system including acombination of a condenser lens 6, an interference filter 7, a quarterwave plate 8, a polarizer 9, a focusing lens 10 and a photodetector 11is additionally provided and at the same time, an numerical processingunit 17 capable of concurrently operating signals from the plurality ofcircularly polarized light detecting systems is added. By the sixthembodiment, a scanning image in the form of a luminance signalindicative of an operation result by the numerical processing unit 17can be obtained. In FIG. 10, only the two circularly polarized lightdetecting systems are depicted only for convenience of illustration butactually, four circularly polarized light detecting systems are used inthe sixth embodiment. Obviously, the number of the circularly polarizedlight detecting systems can be changed as necessary.

In the first to fifth embodiments of the present invention set forth sofar, information about a magnetization component in the direction of thecircularly polarized light detecting system is provided but according tothe sixth embodiment of the present invention shown in FIG. 10,distribution of directions of magnetization can be known in greaterdetail by changing the method of operation by the numerical processingunit 17. FIG. 11 diagrammatically shows results of observation carriedout using iron single crystal as the specimen 51. As is clear from anobservation example of FIG. 11, according to the sixth embodiment of thepresent invention shown in FIG. 10, the magnetization state of thespecimen 51 can be obtained in combination with magnetizationdirections. It should be noted that the method of obtaining a luminancesignal of a scanning image by applying the numerical processing processto signals from the plurality of circularly polarized light detectingsystems can obviously be applied not only to the sixth embodiment of thepresent invention described with reference to FIG. 10 in which theelectron beam 2 is scanned but also to the fifth embodiment of thepresent invention described with reference to FIG. 9 in which thespecimen holder 5 is scanned.

Next, a seventh embodiment of the present invention will be describedwith reference to FIG. 12. In FIG. 12, instead of adding the circularlypolarized light detecting system as in the sixth embodiment of thepresent invention described with reference to FIG. 10, a reflectionmirror 18 is provided and reflection light therefrom is guided to acondenser lens 6. Here, by making a light path for circularly polarizedlight from the reflection mirror 18 different from that for circularlypolarized light incident directly on the condenser lens 6 in thecircularly polarized light detecting system, the two circularlypolarized light rays can be detected by different photodetectors 11. Byprocessing signals obtained from these photodetectors 11 by means of annumerical processing unit 17, observation images similar to those in thesixth embodiment of the present invention described with reference toFIG. 10 can be obtained.

For the light collecting method using the reflection mirror 18 as in theseventh embodiment of the present invention shown in FIG. 12, variouskinds of construction other than that of the seventh embodiment can beconceived. The number of the optical element such as the condenser lens6 or the reflection mirror 18 for collecting light from the specimen 51may be increased as necessary. In this case, a photodetector 11 isprovided in association with each optical element to form one set oflight detecting optical system. In each set of light detecting opticalsystem, it is important that the optical axis of the optical element andassociated photodetector be adjusted and set such that light from anoptical element of a different set is not incident to thatphotodetector. In any case, as compared to the construction in which theplurality of circularly polarized light detecting systems are providedas in the sixth embodiment of the present invention shown in FIG. 10,the equipment construction for detection of circularly polarized lightcan advantageously be compact.

Next, an eighth embodiment of the present invention will be describedwith reference to FIG. 13. In FIG. 13, a rotation unit 19 for applyinginclination and rotation to the specimen holder 5 and acontrolling/processing unit 20 for controlling the rotation unit 19 andincident energy of electron beam 2 upon the specimen 51 and at the sametime, for processing signals from an numerical processing unit 17 isadded to the sixth embodiment of the present invention described withreference to FIG. 10. As has already been described with reference toFIG. 3, the efficiency of generation of circularly polarized lightstrongly depends on the energy of electron beam 2. More specifically,the lower the energy of electron beam 2, the higher the generationefficiency tends to be and therefore, the electron beam 5 being incidenton the specimen 51 and penetrating into the interior gradually losesenergy and the circularly polarized light generation efficiency ismaximized immediately before the stoppage. Through the use of thisnature, magnetization information at different depths can be obtained bychanging the incident energy of electron beam 2 on the specimen 51. Byutilizing this in combination with observation as viewed in variousdirections based on the rotation unit 19, three-dimensional distributionof magnetization can be obtained through computed tomography (CT)process. To this end, necessary controlling of the direction of thespecimen holder 5 and the energy of the electron beam 5 and necessaryprocessing for reconstruction of three-dimensional magnetizationdistribution by applying the tomography process to obtained data can becarried out with the controlling/processing unit 20 in accordance withthe procedure shown in FIG. 14. Thus, according to the eighth embodimentof the present invention, thorough magnetization distribution of thespecimen 51 can be obtained.

The equipment construction capable of materializing the presentinvention is not limited to the previously-described eight embodiments.For example, while in the foregoing embodiments, the circularlypolarized light detecting system including a combination of thecondenser lens 6, interference filter 7 or spectrometer 12, quarter waveplate 8, polarizer 9, focusing lens 10 and photodetector 11 is used fordetection of circularly polarized light but another detector differentlyconstructed can be utilized without impairing the essence of the presentinvention, provided that it has the function of detecting circularlypolarized light. Further, another electron microscope of anyconstruction can obviously be realized without impairing the essence ofthe present invention, provided that it has the function of detectingcircularly polarized light due to MCD generated from a part of specimen51 irradiated with the electron beam 2.

Finally, FIG. 15 shows, as a ninth embodiment, an apparatus in which themechanism for measuring a magnetization state of a specimen according tothe present invention is carried on a general-purpose scanning electronmicroscope (so-called SEM). In the SEM, an electron source 1, anelectrode group 26 for accelerating an electron beam 2 emitted from theelectron source 1, a magnetic lens 27 for focusing the electron beam 2,a deflecting electrode 31 for scanning the electron beam 2 in xdirection on the surface (assumed to be xy plane) of a specimen 51 and adeflecting electrode 32 for scanning the electron beam 2 in y direction,an objective lens 4 for irradiating the electron beam 2 on the surfaceof the specimen 51, a specimen holder on which the specimen is carried,and an XY stage 53 for moving the specimen holder 5 along the xy planeare arranged in a vacuum column 100 as shown in FIG. 15. The deflectingelectrodes 31 and 32 are controlled by an electron beam scanning controlunit 33 so that the electron beam 2 may be scanned on the surface of thespecimen 51. Secondary electrons generated from the specimen 51 underirradiation of the electron beam 2 are detected by an electron detector112 and a detection signal is amplified by an amplifier 113 and inputtedto a signal processing unit (or electronic computer) 115. Further,X-rays (characteristic X-rays) generated from the specimen 51 isdetected by an X-ray detector 114 and similarly inputted the signalprocessing unit 115. The signal processing unit 115 forms a secondaryelectron image or an X-ray image (so-called SEM image) of the specimenin correspondence to a deflecting electrode control signal from theelectron beam scanning control unit 33 and a secondary electron signalor an X-ray signal from the specimen. The above is the well-known basicconstruction and function of the SEM.

The SEM of FIG. 15 is added with the magnetization state measuringfunction of the present invention to have structural features as below.A light detecting optical system for measuring light (circularlypolarized light) generated from the specimen 51 under irradiation of theelectron beam 2 is provided between the objective lens 4 (the finalstage of the electron optical system for irradiating the electron beamon the specimen 51) and the specimen holder 5. But the construction ofthe light detecting optical system is simplified as compared to thepreviously-described embodiments by including only a condenser lens 6for collecting light from the surface of the specimen 51, a focusinglens 10 for focusing the collected light, and a the photodetector 11 fordetecting the focused light. The optical element and the detector areplaced on an arm of an optical system holder 61 which is movedsubstantially along the outer periphery of the specimen holder 5 byrotating a gear 62 by means of an optical system holder rotating unit63. Namely, the optical system holder is moved such that the opticalaxis of the light detecting optical system is rotated substantiallycentrally of the optical axis of the previously-described electronoptical system. The light emitted from the specimen 51 is detected bythe photodetector 11 of the light detecting optical system and inputtedto a signal processing unit (electronic computer) 111. The signalprocessing unit 111 forms a specimen image in correspondence to adeflecting electrode control signal from the electron beam scanningcontrol unit 33 and a light signal from the specimen. In addition toformation of the specimen image and display thereof on a display, thesignal processing unit (electronic computer) 111 controls the opticalsystem holder rotating unit 63 to set the position of the specimen 51relative to the light detecting optical system. On the other hand, aninsulating layer 52 is interposed between the specimen holder 5 and theXY stage 53 and a potential applying unit 21 is connected to thespecimen holder 5. The potential applying unit 21 includes a variablepower supply and can adjust the potential of the specimen 51 on thespecimen holder 5 between earth potential (0 eV) and desired negativepotential. Normally, the electron source 1 is applied with a negativehigh voltage (-1 to -30 kev) and therefore, when the specimen 51 is atearth potential, the electron beam 2 is irradiated on the specimen 51while being accelerated by a potential difference of from 1 to 30 keV.This electron beam irradiating condition is suitable for detectingsecondary electrons and characteristic X-rays and observing SEM imagesbut is unsuitable for observing the magnetization state of the specimenaccording to the invention as has already been described. Then, thepotential applying unit 21 is controlled by a power supply controller211 in accordance with an object to be observed so that a negativevoltage which is approximately several eV higher than the acceleratingvoltage of the electron beam may be applied to the specimen holder 5during the magnetization state observation of the specimen according tothe present invention. Through this, the electron beam 2 is deceleratedfrom kilovolt order to several-volt order between the bottom surface ofthe objective lens 4 at earth potential and the specimen 51 applied withthe negative voltage. The deceleration is effective as has already beendescribed with reference to FIG. 3. It must be noticed that when anegative voltage equal to or less than the accelerating voltage isapplied to the specimen 51, the magnetization state of the specimencannot be measured.

Incidentally, the construction of the light detecting optical system canmore simplified in the apparatus of the present embodiment (embodiment9) than in the other embodiments because the light detecting opticalsystem is made to be rotatable relative to the specimen holder 51 andthis is on the following ground. In the present invention, thecircularly polarized light emitted from the specimen irradiated with theelectron beam is detected to measure magnetization information of thespecimen and according to properties of the magnetic specimen emittingthe circularly polarized light, that is, magnetic circular dichroism(MCD), the detection intensity of the circularly polarized light dependson the relation between the direction of its detection and themagnetization direction of the specimen and is maximized when the twocoincides with each other. It is clear from this that when the lightdetecting optical system moves relative to the specimen holder 51(especially, along the outer periphery of the specimen holder 51), thedetection intensity of the circularly polarized light changes with thepositional relation between the light detecting optical system and thespecimen holder 51. Accordingly, magnetization information of thespecimen (namely, an image based on the circularly polarized light) canbe extracted from a difference between images at different locations (adifference image) by sequentially changing the arrangement of the lightdetecting optical system relative to the specimen holder 51 and scanningthe specimen 51 with the electron beam each time the arrangement ischanged to form an image by detecting light signal from thephotodetector 11 while scanning the electron beam. Obviously, fordetection of the magnetization information, it is important that theincident electron beam be decelerated suitably by thepreviously-described potential applying unit 21. Further, in order tosteadily suppress noise components liable to interfere with themagnetization information of the specimen, a deflecting componentseparating means (for example, a quarter wave plate and a polarizer or apolarizing prism) may be provided in the light detecting optical systemas in the other embodiments. In the apparatus of FIG. 15, the specimenholder 5 is moved relative to the light detecting optical system but thespecimen holder 5 may be moved (rotated) relative to the light detectingoptical system as in the apparatus of FIG. 13 to attain the same effectand in that case, too, the construction of the light detecting opticalsystem can be simplified. In other words, the embodiment 9 isstructurally featured in that the position control means is providedwhich changes (namely, controls and sets) the relative positionalrelation (arrangement) between the specimen holding means for holdingthe specimen and the light detecting means for detecting light from thespecimen.

We claim:
 1. An electron microscope having an electron source foremitting an electron beam, an electron optical system for focusing theelectron beam from said electron source, a specimen holder on which aspecimen is carried, deflecting means for irradiating said electron beamon the specimen carried on said specimen holder, and decelerating meansprovided between said specimen holder and said electron optical systemfor decelerating and irradiating the electron beam on the specimen, saidelectron microscope comprising a detecting optical system including aquarter wave plate and a polarizer which separate and detect a polarizedcomponent of an electromagnetic wave of circular polarization from aspecimen carried by said specimen holder.
 2. An electron microscopeaccording to claim 1, further comprising magnetic field applying meansprovided on said specimen holder for applying a magnetic field to aspecimen carried by said specimen holder.
 3. An electron microscopeaccording to claim 1, further comprising temperature setting meansprovided on said specimen holder for setting a temperature of a specimencarried by said specimen holder.
 4. In an electron microscope, a methodcomprising the steps of accelerating and focusing an electron beam,deflecting the focused electron beam to a predetermined position,decelerating the accelerated electron beam, irradiating a deceleratedand focused electron beam on a specimen, detecting circularly polarizedlight emitted from a magnetization area of said specimen, and forming animage by detecting a signal of said circularly polarized light inregistration with an electron beam irradiated position on said specimen.5. An electron microscope method according to claim 4, wherein in saidstep accelerating and focusing the electron beam, the acceleration ofthe electron beam is carried out by setting energy of said electron beamto 100 eV or less.